1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that has a main pole and a shield.
2. Description of the Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of a recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of a recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure where a read head unit having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head unit includes a coil and a main pole. The main pole has an end face located in a medium facing surface facing a recording medium. The coil produces a magnetic field corresponding to data to be written on the recording medium. The main pole allows a magnetic flux corresponding to the magnetic field produced by the coil to pass, and produces a write magnetic field from its end face.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). The slider is designed to slightly fly over the surface of a recording medium by means of an airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium.
Here, the side of positions closer to the leading end relative to a reference position will be defined as the leading side, and the side of positions closer to the trailing end relative to the reference position will be defined as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
The magnetic head is typically disposed near the trailing end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In particular, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks in the neighborhood of a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing. In the present application, this phenomenon will be called unwanted erasure. Unwanted erasure includes adjacent track erasure (ATE) and wide-area track erasure (WATE). To achieve higher recording density, it is necessary to prevent unwanted erasure.
In order to prevent unwanted erasure induced by the skew and achieve higher recording density, it is effective to provide a write shield in the vicinity of the main pole. For example, U.S. Pat. No. 6,954,340 B2 discloses a magnetic head including a write shield having an end face that is located in the medium facing surface to wrap around an end face of the main pole.
A magnetic head including a write shield is typically provided with a return path section for connecting the write shield to a part of the main pole away from the medium facing surface. One or more spaces are formed between the return path section and the main pole. A coil or coils are provided to pass through the one or more spaces. The write shield and the return path section have the function of capturing a magnetic flux that is produced from the end face of the main pole and spreads in directions other than a direction perpendicular to the plane of the recording medium, so as to prevent the magnetic flux from reaching the recording medium. The write shield and the return path section also have the function of allowing a magnetic flux that has been produced from the end face of the main pole and has magnetized the recording medium to flow back to the main pole. A magnetic head having the write shield and the return path section is capable of preventing unwanted erasure and capable of providing further improved recording density.
The position of an end of a record bit to be recorded on a recording medium depends on the position of the trailing-side end of the end face of the main pole located in the medium facing surface. To define the position of the end of the record bit with high accuracy, it is therefore effective to form the end face of the write shield to include an end face portion located on the trailing side relative to the end face of the main pole.
As the frequency of write signals is increased in order to provide higher recording density, it is required of the magnetic head to provide an improved rate of change in the direction of the magnetic flux produced from the end face of the main pole. To satisfy this requirement in the magnetic head having a write shield, it is effective to form the end face of the write shield to include an end face portion located on the trailing side relative to the end face of the main pole. In addition to this, it is particularly effective to provide the return path section with a yoke layer located on the trailing side relative to the main pole and to reduce the length of a magnetic path that connects the write shield and the main pole to each other through the yoke layer. To that end, it is effective to reduce the number of turns of the coil passing through the space formed between the main pole and the yoke layer. However, this would cause a shortage of magnetomotive force produced by the coil, thereby hindering the main pole from producing a write magnetic field of sufficient magnitude.
As such, it has conventionally been difficult to allow the main pole to produce a write magnetic field of sufficient magnitude while reducing the length of a magnetic path that connects the write shield and the main pole to each other through a yoke layer located on the front side in the direction of travel of the recording medium (i.e., the trailing side) relative to the main pole.